Such plant and aspects of the construction and theory of operation of the individual units of the plants, are known in principle, for example from "Stahl und Eisen" (Steel and Iron) 109, (1989), No. 22, pages 1047 to 1056, expressly incorporated herein by reference. The production of raw steel is in that case carried out in an electric-arc furnace or a converter. The molten steel is then fed to a station for the secondary metallurgical processing for completion of the processing, and is finally cast into ingots in a continuous casting plant.
Another such processing sequence is also known from Mannesmann Demag Huttentechnik Prospectus 6.13.3.11 E 08.09.2000, expressly incorporated herein by reference, which discloses a VOD plant used as unit for the secondary metallurgical processing, as shown in FIG. 1 and the accompanying descriptive text.
In that case, the size of the individual components of the plant and their respective capacities are selected so that for a given output, a reliable flow of material within the processing sequence is assured. The course of the processing within the VOD station is explained with reference to FIG. 1, in which the process is broken down into phases A-F.
Phase A corresponds to the time for conducting or guiding the ladle to the place of processing. During this phase, the connection of inert gas is set up, the scavenging intensity is adjusted and the vessel is covered with a lid that is lined with a fire-proof material or water-cooled. The latter reduces the time in the present example by more than half.
Phase B corresponds to the time of the actual vacuum refining. An initial Carbon (C) content of 0.60% and a Silicon (Si) content of 0.20% is assumed for V2A quality steel. It is also to be understood that steels having varying alloy and impurity contents, i.e. differing in analysis, require shorter or longer processing times which must be taken into account.
Phase C corresponds to the boiling out time following the oxygen refining.
Phase D corresponds to the time for the feeding of the slag former and the reduction agent. In the event of use of a cover having fire-proof material, it is to be removed during this phase, in contradistinction to the case where a water-cooled cover is installed in the plant, which requires more time for removal.
Phase E corresponds to the reduction time, the duration of which depends on various requirements such as reduction, degassing and desulfurization.
Phase F corresponds to the time for correction of the analysis as well as the measurement of the temperature, together with the time for individual activities such as sampling, temperature measurement, alloying, the addition of cold scrap metal and covering of the ladle.
In the context of the production facilities arranged in front and behind of the processing apparatus, the known variants shown in FIGS. 2 to 4 are also possible.
The first variant, shown in FIG. 2, shows the original processing sequence with only one vacuum station. The second variant, shown in FIG. 3, provides for the final handling of the melt in a separate scavenging station.
The third variant, shown in FIG. 4, contains a second processing station. A further reduction of the cycle sequence duration is limited by the availability of the traditional single vacuum pump system, which ordinarily consists of a water ring pump and steam jet.
These known concepts of the processing sequence consisting of a melting facility, a VOD plant, and a casting facility do not represent fundamental solutions to the problem of lengthy net cycle times, and do not set forth a simple, generally applicable method for reducing the cycle time to attain or approach the desired short cycle times for melting and casting facilities. Additionally, these known solutions do not undertake to adapt one processing phase of the processing to another. Thus, changes in the known processing lines, after they have been established, were possible only by including an expensive additional metallurgical installation or by shifting of the finishing time of the melt toward the reduction processing in a separate scavenging stage. The overall prior art system is also inflexible with respect to changes in metallurgical or casting procedures which may have an effect on the cycle time of the individual stages in the sense of shortening these cycle times.
The problems presented by the prior art systems consist therefore of finding a solution which assures a high degree of flexibility and an adaptation of the VOD processing time to the cycle times of the melting and casting facilities arranged prior and subsequent to the processing stage.
The present invention proceeds from a known VOD plant. This consists generally of a combination of water ring pumps and the actual core of the vacuum plant, the steam jets.